I propose to investigate the life cycle distribution of cultured mammalian cells under various conditions of hypoxia and pH, and also after treatment with combinations of hyperthermia and x-rays. The oxygen concentrations employed will be in the range of 50 ppm to 600 ppm in the gas phase. The pH range will be from 6.4 to 7.4. Hyperthermia will either precede, follow, or be applied simultaneously with x-irradiation. Life cycle distributions after various periods of time under these conditions will be obtained by the method of flow cytometry. These will be verified by conventional techniques of labeling index, mitotic index, and percent labeled mitoses. In order to determine the distribution of the viable cells after these treatments, a method will be used which gives colony survival from parallel cultures treated in various ways with Colcemide and high concentrations of 3HTdR (tritium suicide). Prior to using flow cytometry for analysis, I will investigate the importance of Colcemide and hydroxyurea for the staining properties of DNA. Also, the G2/G1 ratio will be precisely determined so computer analysis can be accurately accomplished.